Packaging machines and related methods for forming, filling and sealing flexible, pillow-shaped bags made from a continuous web of packaging film after being formed into a tube are well known. These machines/methods are in wide use to package a variety of loose products, such as snack foods, frozen foods, candies and the like. One of the most successful approaches for forming these bags calls for the use of a continuous, but variable film feed in conjunction with a constant motion oscillating carriage for the stripping/sealing jaws that extend across the feed path of the tube.
The state of the art of this type of prior arrangement includes a sophisticated drive mechanism to oscillate the carriage in a constant, relatively high speed motion. A programmable controller serves to vary the feed of the tube so that an optimum rate of up to 120-140 bags per minute can be successfully obtained in a very reliable manner. The maximum speed of the carriage determines the high output of this machine. The operation of the sealing jaws to form the cross seals of the tube, and all of the other ancillary functions, track the carriage motion through the controller so that the entire packaging process operates in a highly efficient manner. This type of form-fill-seal bagmaker and related method is set forth in several patents assigned to the present applicant, one such patent being entitled "Continuous Vertical Form- Fill-Seal Packaging Machine with constant motion carriage", U.S. Pat. No. 5,533,322, issued Jul. 9, 1996.
While this prior art packaging machine and related method outperforms all other continuous machines that we are aware of on a wide variety of products, especially light weight loose products such as potato chips, there is a need for still higher speed with more efficient cross sealing, including with product stripping. Similar operation advantage is desirable in related endless material handling systems.
While the continuous film feed, such as with opposed feed belts is well established and perfected, for many years others have suggested making bagmakers with sealing jaws that move in a full 360.degree. circular, or modified circular path, so that the sealing jaws do not have to reverse direction at the top and bottom of the tube sealing operation. Some success has been experienced by machines of this type in the past, such as illustrated in the Taylor et al. U.S. Pat. No. 4,663,917, issued May 12, 1987. In this particular arrangement, the sealing jaws are mounted on arms that continuously counter-rotate through 360.degree. in opposite directions around fixed axes. The strippers are extensible and spring loaded. They are guided through forced linear motion that compress the springs as the sealing jaws move through the sealing zone. The cams operating the strippers extend through the return zone of the circle as they continue to compress the springs for a total arc of approximately 270.degree., whereupon the stripper jaws are released adjacent the upper end of the sealing zone for repeating the cycle. In this manner, a modified D stripping pattern of movement is established. While having some success in the market, there are drawbacks to this approach in that this is a forced, simulated linear motion of the jaws in the sealing zone. The reliance on cams and springs to force the linear motion causes high stresses and excessive noise in the stripping operation. The high noise level of such a machine is due to the clash of the metal cams with the cam followers that is necessary to force the strippers into the simulated linear motion. Furthermore, the excessive frictional forces, in addition to the force required to compress the high spring rate springs, greatly increases the power consumption of the machine.
Other inventors, even some earlier in time than Taylor et al., such as illustrated in the U.S. Pat. No. 3,629,987 to Klopfenstein, have attempted to make successful continuous cross sealing machines for bagmakers going with the same counter-rotating arm concept. In the '987 patent, there is also a reliance on the sealing jaws establishing a true D profile path. To do this, the counter-rotating arms are mounted for bodily movement on a second arm, that is in turn also pivoted. The object is to simulate straight paths so that they move parallel along the sealing zone of the tube. This arrangement is even more highly complicated and expensive to build and maintain. Plant air is required to activate an air cylinder required to pivot the mounting arms during the simulated straight line movement along the sealing zone.
A few years after the Klopfenstein '987 patent was issued was when inventors came up with the predecessor to the Taylor et al. machine. Insofar as we are aware, the first cam actuated modified D- shaped sealing jaw movement is illustrated in the Beck et al. U.S. Pat. No. 4,120,235. While this camming approach is recognized as broadly being the predecessor to the Taylor et al. '917 approach generating the similar D-shaped paths, the motion is generated by laterally positioned moving, rather than stationary, cams, with cam followers being carried by the sealing jaws. As in the successor '917 approach, the cams that are subject to large mechanical stresses, inherently suffer wear and maintenance problems, consume large amounts of power and are subject to noisy operation due to the clashing of mechanical cams/followers and other parts.
As others have entered the field of continuous form-fill-seal packaging, the noticeable pattern of dealing with 360.degree. sealing jaw and/or stripper movement is simply switching back and forth between the camming approach of Taylor et al. '917 and Beck '235 and the moveable axle approach of Klopfenstein '987. Specifically, the latest entry, Fukuda U.S. Pat. No. 5,279,098, simply reverts to the moveable axes approach of the '987 patent. It has enjoyed limited success by reviving this old technology. However, the same complicated mechanism portends excessive wear of parts, high stresses and high maintenance requirements, high power consumption and noisy operation for its future.
Along the way, there have been others that have proposed similar systems utilizing planetary gear arrangements to move sealing jaws in a circular path while maintaining the operative face of the jaws or material handling grippers facing each other. In the Iain U.S. Pat. No. 4,516,379, grippers are used to mechanically close packages, which grippers are maintained in a face-to-face operative orientation while being moved in opposite rotating circles. Again, the substantially linear movement along the gripping zone is not a natural mechanical motion, but it must be forced by overlapping the circles being generated and compressing springs through a substantial distance. In other words, the inventor relies on spring loaded jaws to accommodate the need for simulated linear movement through the gripping zone. This provides still another form of a D-shaped path of movement. A similar approach later is set forth in the Simionato U.S. Pat. No. 5,778,641 in which sealing jaws are maintained parallel and properly oriented during their counter-rotating paths of movement by planetary gear arrangements. The only difference in this approach over the Iain '379 patent is the use of pneumatic cylinders to provide the simulated linear motion and D-shaped paths in the sealing zone. The generation of an epicycloidal motion to keep the sealing jaws properly oriented through the counter-rotating paths is identical to the earlier Iain '379 teaching.
From the foregoing, it is apparent that there is a need for departure from the conventional thinking of the past with regard to continuous motion sealing. In particular, contrary to conventional thinking where inventors have attempted to improve the cross sealing, or related material handling or gripping functions, by using counter-rotating arms on fixed or movable axes, or cam and mechanical/pneumatic spring combinations, with or without planetary gear sets, a complete departure is in order. An entirely new approach is needed that would give increased speeds to form bags at a rate of up to 180-200 bags per minute. What is needed is a simple and efficient natural mechanical movement that obviates the need for these counter-rotating arms, with or without moveable axes and the cam and spring arrangements. Instead the sealing jaws should move substantially effortlessly in counter-rotating paths synchronized with continuous film speed that does not require variation as in the past.
In addition to the more efficient operation that minimizes power input, the direction that we have envisioned results in a compact and easy to drive system, even utilizing a single servo motor for the entire dual sealing jaw movement. An additional key advance being sought is obtaining maximum reliability by using integrated gear assemblies that automatically provide natural, not forced sealing jaw movement, alignment and synchronization. Our approach endeavors to obtain substantially increased linear sealing movement of the sealing jaws or other material handling components within its broadest aspects. It should provide travel through fall, counter-rotating cycles without the use of mounting arms, operating cams, pneumatic cylinders or the like. Our goals include providing a built in self regulating movement through opposed gear assemblies that move the sealing jaws in smooth polygonal paths, rather than the prevalent forced, modified D-shaped paths of the prior art.
Also of substantial advantage would be to create jaw motion in the sealing area that is a substantially straight line and extends over the maximum parallel trajectory in the zone. At the same time, the jaws are to remain in perfect forward orientation facing the plastic tube to be sealed. The extended zone allows better control of the heat and pressure needed to heat seal the plastic tube, or perform other, similar gripping functions. At the same time, a gentle mating of the jaws rather than harsh clashing is desirable, made possible by a slight convexity built into the polygonal path in the sealing zone. At the same time avoiding any need for crucial timing functions brought on by variable film feed speeds is to be avoided. As an additional feature, we are looking for full, unforced mechanical squeeze pressure between the jaws so that reliance on heavy, extended length mechanical springs, pneumatic cylinders or the like, that tend to be weak and variable, can be avoided. In addition, we are looking for insuring a companion full motion, positive stripping action to mate with the sealing jaw movement.